RE: [EnergyPlus_Support] Selecting the ASHRAE baseline

Nick and Arpan,

The CIR corresponds to INQUIRY Number 1600.

Here it is:

9/27/2006 -

Credit Interpretation Request
Our question deals with selecting the most appropriate HVAC system baseline for our project.
Our project is a 3-story, 40,000 sf office building. It includes 10,000 sf parking, and 30,000 sf tenant improvement office and core space. Most of the offices and all core spaces will be served by a single VAV system consisting of a rooftop packaged air conditioning unit and electric resistance reheat at series fan-powered boxes in each zone. The rooftop unit delivers low-temperature supply air to the spaces, reset to a temperature dictated by the zone requiring the greatest amount of cooling.
The rooftop unit also contains a gas furnace, which provides heating for the following infrequent scenarios:
1. During night low limit control, when three perimeter zones and one interior zone on any floor fall below the night low limit temperature setpoint.
2. During morning warmup, when outside air temperature is below an adjustable setpoint.
Virtually all other heating needs are served by the electric resistance heaters at the series fan-powered boxes. Based on this predominant use of electric resistance heat, we have categorized our heating source as "electric" and have selected a "packaged rooftop heat pump" (System 4) for our baseline HVAC system per ASHRAE 90.1-2004 Appendix G Table G3.1.1A.
Four considerations affected our interpretation of which baseline to use:
1. Heating source for the design. The two scenarios in which heating is provided by the gas furnace, identified above, do not comprise a significant proportion of the total heating required by the building. Rather, the majority of the building heating (approximately 90% of the total annual heating energy), is provided by electric resistance reheat at the fan-powered boxes.
2. Avoidance of fuel-switching. Although a "packaged rooftop air conditioner" with fossil fuel furnace (System 3) is specified for design buildings using a "fossil/electric hybrid" HVAC system, use of a System 3 baseline appears to create a situation of fuel-switching. Our design building heating source is predominantly electric, whereas the System 3 baseline heating source is a fossil fuel furnace.
3. Consideration of reheat strategy for both design and baseline models. The System 3 "packaged rooftop air conditioner" with fossil fuel furnace might be considered a reasonable baseline for comparison to our design building if the baseline system included electric reheat at each zone. However, based on Appendix G rules and guidance provided in the ASHRAE 90.1-2004 User's Manual, the System 3 HVAC system must be represented with a separate packaged single zone unit for each thermal zone in the baseline model, which implies that no zone level reheat is necessary.
4. Consequence of baseline requirement on future building HVAC designs. If the intent of Table G3.1.1A is to require a System 3 baseline for our particular design, the baseline has the effect of encouraging replacement of infrequently-used gas furnace heaters in rooftop units with less energy-efficient, electric heaters. Such a design change could occur relatively easily, especially during value engineering. These reasons - lower initial cost of an electric heater and the opportunity to show higher energy cost savings relative to an electric heat pump baseline - would seem to provide a compelling reason for changing the design by eliminating the gas furnace. It does not seem reasonable that this type of small design change to a rooftop packaged unit, replacing gas heat with electric, should become a pivotal issue in determining the correct baseline for LEED calculations.
For these reasons, we consider System 4 to be the appropriate baseline for our project. Is this an acceptable baseline selection?

10/23/2006 -

Ruling
The project team is seeking clarification regarding the Baseline Building system type selection. The proposed design system is heated predominantly by electric resistance reheat controls, but includes some fossil fuel heating for morning warm-up and night-cycle control. Based on the size and number of floors for the building, the Baseline system type selection will be either System 3 (PSZ-AC) or System 4 (PSZ-HP).

The functions described for the gas furnace appear to be consistent with the functions accomplished with a preheat coil. Per ASHRAE 90.1-2004 Section G3.1.2.3, if the HVAC system in the proposed design has a preheat coil, and a preheat coil can be modeled in the baseline system, the baseline system shall be modeled with a preheat coil controlled in the same manner as the proposed design. The ASHRAE User’s Manual states “This means that adding a preheat coil is not something that can be credited toward a building performance rating.”

System 4 is a valid selection for the Baseline Building system, assuming that the project does not attempt to take credit for natural gas heating versus electric heating in the Proposed Building energy model. If the energy modeling software is incapable of modeling a gas furnace preheat coil for PSZ-HP systems, then the heating source would have to be labeled “Fossil/Electric Hybrid”, and the Baseline system type would be System 3.

Regards,

Demba.

From: Nick Caton [mailto:ncaton@xxxxxxxxxxxxxxxx]
Sent: Friday, March 25, 2011 5:12 PM
To: Arpan Bakshi
Cc: Demba Ndiaye
Subject: RE: [Equest-users] electric heating issues

Hey Arpan,

Demba is the one who just brought that CIR to my attention in her post yesterday. I haven’t sought it out yet, but she may be able to quickly point you in the right direction (?).

Otherwise, there’s always this fancy new search engine everyone’s excited about =): https://www.usgbc.org/leedinterpretations/lilanding.aspx

If you do come across it I’d be interested in a link too if only out of curiosity.

Thanks and good luck!

~Nick

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com

From: Arpan Bakshi [mailto:arpanbakshi@xxxxxxxxx]
Sent: Friday, March 25, 2011 3:54 PM
To: Nick Caton
Subject: Re: [Equest-users] electric heating issues

Nick, do you have a CIR name/number?

We have an issue with ground source heat pump in which natural gas boiler is used for a minor reheat function and all else is electric.

On Fri, Mar 25, 2011 at 1:41 PM, Nick Caton <ncaton@xxxxxxxxxxxxxxxx> wrote:

Neat discussion – looks like my position on this is going to go against the grain a bit =)!

First, the CIR Demba referenced looks like something of prime interest… I understand CIR’s don’t exactly hold water with the current LEED reviewer-ship, but it would sure help at times know whether history is on your side…

I can offer some recent directly related experience: Without having been aware of that particular CIR, I recently wrapped up a LEED project with HVAC gas furnace heating used only for morning warmup/preheat at the central AHU. The proposed system otherwise was effectively well-described by baseline system #6, with electric reheat accomplishing the vast majority of conditioned air heating (substantial heat recovery was a part of this), so I used baseline system #6. The reviewer on first pass stated the baseline needed to be system #5 due to the presence of gas heating, and I composed a comment response substantiating why the electrical heating was the “predominant condition,” referencing the corresponding subnote to Table G3.1.1A… Had I been aware of a CIR to the same effect I would have included a reference. The model has since been approved and all resubmitted credits have been awarded =).

I can’t guarantee your reviewer will consider the issue at hand in the same fashion, but in these sorts of cases applying an “all gas” baseline system against a “99% electric” proposed system can make for a truly unfair comparison when the utility rates are quite different.

For those not keeping score, I don’t use a term like “unfair” lightly or often.

A completely literal reading of 90.1-2007 Table G3.1.1A may lead you to use system #5 over #6, and for that reason it’s not wrong to say that’s a “right” answer. On the other hand a case can be made, particularly if you can demonstrate that the HW preconditioning is a small fraction of the total space heating energy, that the intent of the “predominant condition” subnote speaks directly to this instance and can present another “right” answer. Without using a word like “unfair,” be prepared to intelligently discuss why system #6 is fundamentally a better baseline for the purposes of establishing a performance rating against your proposed systems.

Finding and referencing that CIR Demba mentioned wouldn’t hurt either… =)

~Nick

PS: On a related tangent… how do you guys find past CIR’s? I can only ever get so far using google – is there some kind of archive currently within LEED online I’ve been missing?

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com

From: equest-users-bounces@xxxxxxxxxxxxxxxxxxxxx [mailto:equest-users-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Will Mak
Sent: Thursday, March 24, 2011 1:56 PM
To: Carol Gardner
Cc: equest-users@xxxxxxxxxxxxxxxxxxxxx

Subject: Re: [Equest-users] electric heating issues

Sorry, I thought I put down that the baseboard and VAV reheat coils were electrical, not hot water. The hot water is only for the preheat.

William Mak, LEED Green Associate
Mechanical Design Engineer

EPSTEIN
Architecture
Interiors
Engineering
Construction

600 West Fulton Street
Chicago, Illinois 60661-1259

D: (312) 429-8116
F: (312) 429-8800

E: wmak@xxxxxxxxxxxxxxxxx
W: www.epsteinglobal.com

� Epstein is a firm believer in sustainability. We ask that you please consider the environment before printing this e-mail.

From: Carol Gardner [mailto:cmg750@xxxxxxxxx]
Sent: Thursday, March 24, 2011 1:41 PM
To: Will Mak
Cc: Rob Hudson; equest-users@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [Equest-users] electric heating issues

Hi Will,

Sorry to say but I agree with Rob and Bill. If you are providing heated hot water to the baseboards then you are using a hybrid system. Maybe I am missing something, but it seems pretty clear.

Carol

On Thu, Mar 24, 2011 at 11:10 AM, Will Mak <wmak@xxxxxxxxxxxxxxxxx> wrote:

I thought the heating system only referred to the heating source itself? (not including preheat fuel source??)

E: wmak@xxxxxxxxxxxxxxxxx
W: www.epsteinglobal.com

� Epstein is a firm believer in sustainability. We ask that you please consider the environment before printing this e-mail.

From: Rob Hudson [mailto:rdh4176@xxxxxxxxx]
Sent: Thursday, March 24, 2011 12:23 PM
To: Will Mak
Cc: Bishop, Bill; equest-users@xxxxxxxxxxxxxxxxxxxxx
Subject: Re: [Equest-users] electric heating issues

as per the baseline system discussion, i would use System 5. If you read the 90.1 manual, it says if you use a fossil/electric hybrid heating system to implement System 5 in the baseline.

Rob

On Thu, Mar 24, 2011 at 12:14 PM, Will Mak <wmak@xxxxxxxxxxxxxxxxx> wrote:

See comments below, thanks!

E: wmak@xxxxxxxxxxxxxxxxx
W: www.epsteinglobal.com

� Epstein is a firm believer in sustainability. We ask that you please consider the environment before printing this e-mail.

From: Bishop, Bill [mailto:wbishop@xxxxxxxxxxxxxxxxx]
Sent: Thursday, March 24, 2011 10:21 AM
To: Will Mak; equest-users@xxxxxxxxxxxxxxxxxxxxx
Subject: RE: [Equest-users] electric heating issues

Will,

The first thing I would do is reconsider your selection of System 6 for the Baseline. Since you have gas boilers for preheat, I would choose System 5. System 6 is all electric, but you say your baseline gas consumption is high, so you are currently modeling gas boiler(s) in the baseline. Unfortunately, if you go with System 5, your baseline reheat will be hot water which will save cost versus your proposed design.

Yes, I am modeling the gas boilers in the baseline purely for preheating. So you are saying that because I am modeling gas boilers (even though they are just for preheat), I technically can run with System #5 for my baseline model?

Since both your baseboards and your reheat are electric in the proposed design, your high electric use is probably not a baseboard control issue (provided you are not showing many unmet load hours). One thing to consider is your preheat leaving temperature – making it higher will favor the gas boilers and reduce the zone electric heating. I’m guessing that the requirement for identical preheat coil control in G3.1.2.3 means that you use the same preheat leaving temperature in the baseline and proposed models.

I currently have both models at minimum leaving temperatures for preheat of 60F (which is the design preheat leaving air temp). You would think that because the preheat is pumping out 60F air to the VAV boxes, you would see similar zone heating requirements. However, the proposed design’s zone heating is much higher. Could it possibly be the parallel fan powered boxes that help the baseline model that much?

Make sure you are modeling your ventilation identically between the baseline and proposed models, unless you have DCV.

Yup, I have the same OA cfms for both models

Check your reports to make sure you don’t have a lot of simultaneous heating and cooling going on. Maybe you can increase the cooling supply temperature (and convince the HVAC designer to do it) to the highest allowable temperature that meets cooling and dehumidification loads.

Currently, I have the cooling supply temp at 52.5 F. This was because the design engineer wanted to take advantage of the efficiency of the chillers on the project for cooling energy savings. Perhaps this could be the issue? The cooling temperature is too low that it triggers the reheat/baseboard to kick on all the time??

Your baseline may have similar, or even less, heating load depending on the proposed envelope, due to the reduced lighting load in the proposed design. With electric baseboard and electric reheat, it will be difficult to show much heating savings unless you have a much better envelope or ventilation heat recovery. We should all be red-flagging electric reheat and baseboards whenever we see them on projects.

So you are saying that electric heat/reheat is bad for 90.1 PRM??

Thanks for the response!

Regards,

Bill

William Bishop, PE, BEMP, LEED^� AP | Pathfinder Engineers & Architects LLP

Mechanical Engineer

Error! Filename not specified.134 South Fitzhugh Street Rochester, NY 14608
T: (585) 325-6004 Ext. 114 F: (585) 325-6005

wbishop@xxxxxxxxxxxxxxxxx www.pathfinder-ea.com

P Sustainability – the forest AND the trees. P

From: equest-users-bounces@xxxxxxxxxxxxxxxxxxxxx [mailto:equest-users-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Will Mak
Sent: Thursday, March 24, 2011 10:31 AM
To: equest-users@xxxxxxxxxxxxxxxxxxxxx
Subject: [Equest-users] electric heating issues

Hello all,

I currently modeling a project for LEED NC v2009 submission for a corporate office building that’s roughly 125,000 SF. The proposed design’s primary HVAC system are AHUs + VAVs w/Electric Reheat supplemented with electric baseboard along hot water preheat generated from gas boilers. This system also uses chilled water with very efficient chillers from a DES. The baseboard is suppose to take care of the envelope loads and the VAV electric reheat coils will take care of the rest. Based on the size of the building, the baseline HVAC system shall be System #6: Packaged VAV with PFP Boxes.

I’m pretty down the road on the models and for some reason cannot get savings between the 2 models. The heating energy use on electrical consumption overrides any savings attributed from lighting, site lighting, cooling energy use, etc. Also, I know that in 90.1-2007, preheat must be model identical on the proposed and baseline models. I am having a hard time modeling both to be the same (inputs for preheat capacity are the same but the energy use is different). The gas consumption is significantly higher on the baseline model.

I double checked the loads from both models and the heating/cooling requirements are roughly the same so there’s nothing wrong with the building shell/internal load inputs. Any guidance on how to reduce the consumption on the heating use for electrical consumption would be great! I am confused why the baseline model wouldn’t require similar, if not more, heating requirements and isn’t using more heating use for electrical consumption. Also, guidance to ensure that the preheat is model identical would help too!

Thanks!

Cliffnotes:

Proposed System: AHUs w/VAV Electric Reheat + Electric Baseboard//Chilled Water from DES//Hot Water Preheat

Baseline System: Packaged VAV with PFP Boxes

Issue #1: Heating electrical consumption is super high on proposed model despite similar loads for both models.

Issue #2: Preheat is not being model identical as required from 90.1-2007. Capacity and design inputs are same for building but baseline building is using significantly more gas.

E: wmak@xxxxxxxxxxxxxxxxx
W: www.epsteinglobal.com

� Epstein is a firm believer in sustainability. We ask that you please consider the environment before printing this e-mail.

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Rob Hudson

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Carol Gardner PE

Arpan Bakshi LEED AP BD+C